Electric circuit interrupter



May 9, 1939. R. AUERBACH ET AL ELECTRIC CIRCUIT INTERRUPTER Filed April7, 1938 COMPOSITION COMPRISING EXPLOSIVE MATERIAL PREFERABLY AN ORGANICNITROGEN COMPOUND, CAPABLE OF 3 YIELOING AN ARC-INTERRUPTING GAS WITH ANEXPLOSIVE EFFECT UNDER ARC HEAT AND A PHLEGMATIZER THEREFOR FOR EAMPLEUREA OR ITS DERIVATIVES.

Inventors: Rudolf AueT-bach,

n, m w e h m m, u a B m a m mW .P fl H Patented May 9, 1939 UNITEDSTATES PATENT OFFICE ELECTRIC CIRCUIT INTERRUPTER Rudolf Auerbach,Dahlewitz Hoppegarten, and

Herman Burmeister, Berlin-Spandau, Germany, assignors to GeneralElectric Company, a corporation oi. New York Application April 7, 1938,Serial No. 200,770 In Germany April 7, 1937 .12 Claims.

In a well-known form of circuit interrupter of v the aforesaid type, thearc is drawn in a confining insulating structure, such as a tube formedof material which under the influence of the arc emits gases or vaporstending to extinguish the arc. Inorganic materials such, for example, asboric acid, ammonium alum, etc., have been proposed as the gas-producingmaterial. In these substances water is chemically combined so that,under the influence of the arc, vapors are released for thearc-extinguishing process. It has also been proposed to use aminoplasts(general term for synthetic resins from amido or amino compounds) in theconstruction of arc-confining structures. Aminoplasts contain nitrogenwhich is evolved under the arc heat and tends to extinguish the arc.

More recently, other gas-producing materials or compositions containingthe same have come into prominence for making arc-insulating members.For example, in Burmeister U. S. Patent 2,089,050 is disclosed andclaimed an arc-confining structure composed of oxalic acid; and inBurmeister U. S. Patent 2,089,051 mechanically strong organic material,for instance hard rubber, impregnated with an inorganic material whichupon decomposition yields an arc-interrupting gas and, specifically,with ammonium carbonate or bicarbonate calcium carbonate, etc. Referenceis also made to the copending applications of Paul Nowak, Serial No.200,798, filed April 7, 1938, of Hans Schuhmann, Serial No. 201,410,filed April 11, 1938, and of Vitaly Grosse, Serial No. 200,784, filedApril '7, 1938, all of which applications are assigned to the sameassignee as the present invention. In these co-pending applicationsother solutions to the same general problem of improving circuitinterrupters of the air-break expulsion type are disclosed and claimed.

It is also known to provide switch chambers with explosive materials incartridge form, or else as liquid or vapors, which are caused to explodeand the explosion gases driven between the separating switch contacts.Switches so made, however, have not attained any practical importance,for one reason because the constant storage of large quantities ofexplosive or highly inflammable materlal in or adjacent the switchinstallation is dangerous. Further, numerous problems of design andconstruction are involved, as the-comparatively great and shock-likeexplosive forces must be dependably controlled. This requirescomplicated mechanism, so that the charge of explosive gases which isreleased in the switch chamber will be adequate to extinguish the arcunder a wide variety of service conditions.

Our invention will be set forth in the following description referringto the accompanying drawing, and the features of novelty whichcharacterize our invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

The single figure of the drawing is an elevational view, partly insection, of an electric circuit breaker of the expulsion type to whichthe present invention is applicable.

It is known that various explosive materials disintegrate rapidlywithout forming any residue. In accordance with the present inventionelectric circuit interrupters having insulating structures disposedadjacent and in confining relation to an are formed upon opening thecircuit have walls formed of, or surfaced with compositions comprising acombination of explosive material and phlegmatizing material that slowsup the decomposition of the explosive material. Examples of explosivematerials suitable for the purpose are organic nitrogen compounds as,for instance, nitrocellulose (cellulose nitrate), nitrotoluene, and thelike. The explosive materials may be contained in the walls in powdery,granular or fibrous form. The phlegmatizing materials preferably arecompounds which decompose substantially completely into volatilecomponents (gases and vapors) under the are heat. Advantageously thephlegmatizers may be fusible compounds, such as urea or ureaderivatives, which at the arc temperature form arc-extinguishing gaseswithout depositing carbon. Ammonia substitution products as, forinstance, hexamethylene tetramine may be used; also, aminoplasts such,for example, as ureaor thio-urea-formaldehyde condensation products. Asphlegmatizing materials one may also use compounds which under the archeat form carbon in a nonconductive modification. Examples of suchcompounds are acrylic acid derivatives, especially acrylonitrile andacrylic acid esters, for instance the methyl and ethyl esters of acrylicand methacrylic acid; also, vinyl compounds, especially of the explosivematerial, so that the selectedmaterials will be compatible with eachother.

The explosive decomposition of the explosive materials contained in thewalls of the insulating structure isrestricted, through the addition ofthe phlegmatizing materials, to those points that are exposed directlyto the influence of the layers. serve as a binder for the explosivematerial.

arc. \Therefor the desired decomposition of the layers of the amberwalls exposed to the are heat does not continue through to theunderlying The phlegmatizing material also may In the accompanyingdrawing there is shown merely by way of example an electric circuitinterrupter, more particularly a circuit breaker having means such asthe stationary contact I and the movable rod contact 2, for opening thecircuit so as to form an arc, and an insulating structure 3 forming anarc chamber for closely confining the are between the contacts. Theinsulating structure 3 consists of a tubular member closed at the fixedcontact end and open at the other end for receiving therod contact. Uponopening of the circuit, separation of the-contacts I and 2 causesformation of an arc which decomposes some of the material of the arcchamber walls 3. The gas so formed is under considerable pressure byreason of the comparatively close flt of the rod contact 2 and the tube3, with the result that when the rod leaves the tube a blast'of gasisreleased as indicated for interrupting the arc. g

The following examples illustrate compositions of which the insulatingstructure 3 may be formed in accordance with the present invention:

' A compound of the type CHFC \R wherein R represents a condensed cyclicsystem with nitrogen united to the nucleus, and specifically fibrousvinyl carbazole, is ground without destroying its fibrous structure,with about 1 to 10 per cent by weight of a substance capable of emittingoxygen in the heat of the arc and about 10 to 30 per cent by weight ofan organic compound containing nitrogen and capable of evolvingarc-extinguishing gases with an explosive effect under the are heat. Anexample of such an organic compound is cellulose nitrate having a lownitrogen content (about 10.5 to 11.5 per cent), which material also isknown as pyroxylin. Examples of oxygen-emitting substances which aresuitable for use are inorganic peroxides as, for instance, peroxides ofbarium, magnesium a d the like. Suflicient aminoplast, suchas ureaformaldehyde resin, is incorporated into the mas to form a compositionadaptedto be shaped, to example by molding, extrusion, andso on. moldingor extruding temperatures are kept s low as possible so as to preventdecompositio of the explosive material. The fibrous vinyl carbazoleserves as a rigid carrier of the c ulose gen for oxidizing into carbondio that may be formed during the gasifying process.

If it is desired to form the quenching tubes or filling pins by awinding operation, then the procedure may be as follows: Cellulosenitrate having a nitrogen content of approximately 8 per cent, and incontinuous sheetor fabric form, is coated and impregnated with anamino'plast, and wound into tube shape. In order to increase themechanical strength, the sheet or fabric of cellulose nitrate may besuitably combined with flbrous material. For example, cellulose fibers,especially those resulting from the well-known sulphite process,asbestos fibers and the like may be incorporated in the cellulosenitrate prior to sheeting it. Or, layers of hard fiber, paper, or woolor linen fabric may be alternated with layers of sheet cellulose nitratein forming the tube.

Insulating structures produced by our invention have the advantage ofavery quick and residue-free development of gas in the course of the arcinterruption. At the same time the development of the extinguishing gasis dependent upon the strength and the duration of the arc, and adaptsitself automatically to the value of the current that is to beinterrupted. Special dosing devices are eliminated.- Further, as in eachcase there is an explosive decomposition of only a small part of theexplosive material contained in the walls of the insulating structure,due to the presence of an agent adapted to retard explosion of theexplosive material, the structure is subjected to no shock-like stressand therefore need not have any unusual dimensions. The phlegmatizingmaterial also eliminates danger of a violent explosion which mightdestroy the circuit-interrupting device. 7 What we claim as new anddesire to-secure by Letters Patent of the United States is:

1. An electric circuit interrupter comprising means for forming an arc,and an insulating structure disposed adjacent and in confiningrelation'to said arc, the walls of said structure in proximity to saidare being surfaced with a composition comprising an organic nitrogencompound selected from the class consisting of cellulose nitrate andnitrotoluene, and a phlegmatizer therefor.

2. An electric circuit interrupter including an arc-confining structure,said structure being formed of a substance comprising an organicnitrogen compound selected from the class consisting of cellulosenitrate and nitrotoluene and a material adapted to retard the explosivedecomposition of said compound.

3. An electric circuit interrupter comprising means for forming an arc,and an insulating tubular structure within which said are is drawn, saidtubular structure being in confining relation to'said. arc and havingwalls in proximity thereto formed of a composition comprising cellulosenitrate and a phlegmatizing material adapted to retard the explosivedecomposition of cellulose nitrate in the heat of the are.

4. An electric circuit interrupter comprising means for forming an arc,and an insulating structure disposed adjacent and in confining relationto said are, said insulating structure comprising nitrotoluene and aphlegmatizing material capable of decomposing substantially completelyinto volatile components at the arc temperature and at such temperaturebeing adapted to retard the explosive decomposition of the nitrotoluene.

5. An electric circuitinterrupter including an arc-confining structure,said structure comprising cellulose nitrate and a phlegmatizing materialselected from the class consisting of urea and its derivatives.

6. An electric circuit interrupter comprising means for forming an arc,and an insulating structure disposed adjacent and in confining relationto said arc, said insulating structure being formed of a compositioncomprising fibrous vinyl carbazole, cellulose nitrate and a substancecapable of emitting oxygen in the heat of the arc.

7. An electric circuit interrupter including a tubular arc-confiningstructure, said structure comprising sheet cellulose nitrate coated andimpregnated with an aminoplast.

8. An electric circuit interrupter comprising means for forming an arc,and an insulating structure disposed adjacent and in confining relationto said arc, the walls of said structure in'proximity to said arc beingsurfaced with a composition comprising an organic nitrogen compoundselected from the class consisting of cellulose nitrate andnitrotoluene, a phlegmatizer that will retard the explosivedecomposition of the said nitrogen compound under the heat of the arc,and a substance capable ofemitting oxygen in the heat of the arc.

9. An electric circuit interrupter as in claim 1 wherein thephlegmatizer is an aminoplast.

10. An electric circuit interrupter as in claim 8 wherein thephlegmatizer is an aminoplast.

11. An electric circuit interrupter comprising means for forming an arc,and an insulating structure disposed adjacent and in confining relationto said arc, the walls of said structure in proximity to said are beingsurfaced with a composition comprising a rigid material carrying anorganic nitrogen compound selected from the class consisting ofcellulose nitrate and nitrotoluene, and in addition thereto anaminoplast.

12. An electric circuit interrupter as in claim 11 wherein the rigidcarrier material is fibrous vinyl carbazole and the organic nitrogencompound is cellulose nitrate.

RUDOLF AUERBACH. HERMANN BURMIEISTER.

